Mourners crowded a memorial service for victims of the shooting at Sandy Hook Elementary School in the auditorium of Newtown High School in Newtown, Conn., Dec. 16, 2012. President Barack Obama spoke at the memorial and met privately with families and first responders.

The world reacts a day after the shootings at Sandy Hook Elementary School in Newtown, Connecticut. The massacre of 26 children and adults at the school elicited horror and soul-searching around the world even as it raised more basic questions about why the gunman, 20-year-old Adam Lanza, would have been driven to such a crime and how he chose his victims.